aromatic compounds

Question 1

what are the three pieces of evidence to show benzene does not show the Kekule proposed structure

Answer 1

1 benzene is more stable than expected
2 all C-C bond lengths are the same
3 benzene doesn’t easily undergo addition reactions

Question 2

what does benzene require to react with Br2

Answer 2

catalyst and reflux

Question 3

why is benzene less reactive than expected

Answer 3

the 6 P electrons are delocalised over the ring which stabilises it

Question 4

combustion of methyl benzene produces (flame not product)

Answer 4

a VERY smoky yellow flame
(high carbon to hydrogen ratio)

Question 5

combustion of cyclohexene produces

Answer 5

a smoky yellow flame

Question 6

reaction of methylbenzene with bromine water at room temperature

Answer 6

no reaction (requires a catalyst)

Question 7

reaction of cyclohexene with bromine water at room temperature (observation)

Answer 7

orange solution becomes colourless

Question 8

equation for methoxybenzene with a chloroalkane (with AlCl3 catalyst and heat)

Answer 8

C6H5OCH3 + RCl –> C6H4OCH3R + HCl

Question 9

conditions for methoxybenzene and chloroalkane

Answer 9

heat
AlCl3 catalyst

Question 10

observations of methoxybenzene and chloroalkane (4)

Answer 10

effervescence
damp blue litmus paper turns red
steamy fumes
white smoke with NH3

Question 11

equation for nitration of methoxybenzene

Answer 11

C6H5OCH3 + HNO3 –> C6H4OCH3NO2 + H2O

Question 12

what is an electrophile

Answer 12

a species which can accept a lone pair of electrons

Question 13

which mechanism does benzene react with

Answer 13

electrophillic substitution

Question 14

3 steps of an electrophilic substitution mechanism

Answer 14

1 formation of the electrophile
2 pair of electrons drawn from the ring to form a dative covalent bond with electrophile and reformation of the ring
3 regeneration of the catalyst

Question 15

reagents and conditions for nitration of benzene (electrophilic substitution)

Answer 15

conc nitric acid and conc H2SO4 catalyst
heat at 55 degrees

Question 16

what would happen if nitration of benzene reached above 60 degrees

Answer 16

further substitution of the ring (more nitro groups)

Question 17

reagents and conditions of halogenation of benzene

Answer 17

Br2 and FeBr3 catalyst
or
Cl2 and AlCl3 catalyst

heat

Question 18

reagents and conditions alkylation of benzene

Answer 18

alkyl halide (RCl)
AlCl3 catalyst (or FeBr3 for RBr)

heat

Question 19

why does benzene have a higher boiling point than ethanol

Answer 19

London forces between benzene molecules are stronger than hydrogen bonds between ethanol molecules

Question 20

what are the most suitable conditions for the nitration of phenol

Answer 20

dilute nitric acid at room temperature

Question 21

what does phenol produce with excess bromine water

Answer 21

2,4,6-tribromophenol